This invention relates to a method for forming a patterned aluminum layer on a substrate, and more particularly relates to a method for forming such a pattern by the selective etching of an aluminized web, and also relates to the article resulting from the method.
The formation of patterns by the selective etching of an aluminized web is known from U.S. Pat. No. 4,398,994, issued to Donald E. Beckett on Aug. 16, 1983. In that patent, the pattern is formed in a rapid and continuous manner on an aluminized polymer film by printing the aluminum surface with a pattern of a caustic resistant masking material such as a water-insoluble resin, contacting the surface with a dilute solution of warm caustic to dissolve the exposed aluminum, and washing the spent solution from the film.
The polymer film is typically aluminized by vacuum evaporation, and the thickness of the resultant aluminum layer is said to vary widely, from about 10 to 1000 Angstroms, preferably 300 to 600 Angstroms.
The caustic solution has a concentration of up to about 25 weight percent of sodium hydroxide, preferably about 5 to 10 percent, and is maintained at a temperature of from about 15 to 100 degrees C., preferably about 50 degrees C.
For certain specialized applications, it is desired to form a micropattern of aluminum on a transparent backing such as a polymer film. As used herein, the term "micropattern" is intended to refer to any pattern at least a portion of which has minimum dimensional elements (e.g., lines or dots) of from about 0.2 to 2 mils.
When it is attempted to form such micropatterns by the above described technique, the caustic solution is found to undercut the edges of the mask and attack the underlying aluminum. Depending upon the etching conditions and the line width of the pattern, the underlying aluminum layer can be substantially or entirely removed.
Accordingly, it is an object of the invention to provide a method for producing a pattern of aluminum by the selective removal of aluminum from a substrate.
It is another object of the invention to provide such a method in which a micropattern of aluminum can be produced.
It is still another object of the invention to provide such a method in which the micropattern can be produced rapidly and continuously.